1. Field of the Invention
The present invention relates to a method and an apparatus for forming a deposited film on a substrate by plasma chemical vapor deposition (hereinafter referred to simply as xe2x80x9cplasma CVDxe2x80x9d) More particularly, the present invention relates to a method and an apparatus for forming a functional deposited film on a substrate by plasma CVD, the deposited film being usable as a semiconductor layer for use in semiconductor devices such as semiconductor circuit elements, electrophotographic photosensitive devices (or electrophotographic light receiving members), image input line sensors, image pickup devices, photovoltaic devices (including solar cells), and the like.
2. Related Background Art
Heretofore, as the constituent element members of semiconductor devices such as semiconductor circuit elements, electrophotographic photosensitive devices (or electrophotographic light receiving members), image input line sensors, image pickup devices, or other electronic devices including optical devices, there have been proposed a number of non-single crystalline semiconductor deposited films, for instance, amorphous semiconductor deposited films composed an amorphous material such as an amorphous silicon material compensated with hydrogen atoms (H) or/and halogen atoms (X). Some of these films have been put in practical use
For some of these semiconductor devices in which such semiconductor deposited films are used as the constituents, there are several points which are required to be further improved, particularly in view of their productivity and production cost.
For instance, in the case of producing an electrophotographic light receiving member, it is required to form a large area deposited film having a relatively larger thickness in comparison with that of a deposited film formed in the production of other semiconductor devices. In order to form such deposited film having a large thickness, it takes a relatively long period of time. This situation often results in an increase in the production cost of an electrophotographic light receiving member obtained.
In consequence, there is a demand for providing an improved film-forming method or apparatus which enables to efficiently form a desirable deposited film having a desired thickness so that the productivity of an electrophotographic light receiving member can be improved while improving the efficiencies of various factors related to the production of the electrophotographic light receiving member.
In order to meet such demand, Japanese Unexamined Patent Publication No. 186849/1985 proposes a method for forming a deposited film using a plasma CVD appratus using microwave (hereinafter referred to as microwave plasma CVD apparatus) Particularly, this Japanese document describes a deposited film-forming method using a microwave plasma CVD apparatus, wherein a plurality of electrically conductive cylindrical substrates are arranged in a deposition chamber so as to establish an internal chamber in said deposition chamber, and a film-forming raw material gas is introduced into said internal chamber while introducing a microwave power thereinto, whereby the utilization efficiency of the film-forming raw material gas is improved and the productivity of a deposited film formed is improved.
Besides, U.S. Pat. No. 5,129,359 proposes a method for forming a high quality deposited film by applying an electric field of direct current in a discharge space for producing a plasma to control the potential of the plasma produced.
However, even in the case of such microwave plasma CVD apparatus as above described, there are still several points to be improved. That is, because a microwave power is introduced into the internal chamber from the opposite sides of the internal chamber (from the opposite sides of the arrangement of the electrically conductive cylindrical substrates in other words), a deposited film formed on each of the electrically conductive cylindrical substrates tends to have a variation in the characteristics in a generatrix direction, and the deposited films formed on the plurality of electrically conductive cylindrical substrates are sometimes ununiform in terms of the characteristics.
Such ununiformness in terms of the characteristics exerts an influence to the yield of a semiconductor device produced, and this situation eventually becomes a factor to raise the production cost of a semiconductor device produced even when the production capacity should be improved.
In order to improve this disadvantageous situation, U.S Pat. No. 5,455,138 proposes a deposited film-forming method using a plasma CVD apparatus in which a high frequency power with an oscillation frequency of 20 to 450 MHz is used. In this film-forming method, as well as in the case of the deposited film-forming method described in the foregoing Japanese document, a plurality of electrically conductive cylindrical substrates are arranged in a deposition chamber so as to establish an internal chamber in said deposition chamber, and a film-forming raw material gas is introduced into said internal chamber while introducing a high frequency power with such oscillation frequency (including an oscillation frequency belonging to so-called VHF (very high frequency) band region) thereinto, whereby the utilization efficiency of the film-forming raw material gas is improved and the productivity of a deposited film formed is improved.
However, electrophotographic apparatus (electrophotographic copying machines) in which an electrophotographic light receiving member is used have been rapidly progressed to have a high driving speed, an improved image-reproducing performance capable of providing a high quality image at a high speed, and a prolonged durability. In addition, digital copying machines and color copying machines in which an electrophotographic light receiving member is used have been developed and they have been widely using. In this connection, for an electrophotographic light receiving member to be used in these copying machines, there is an increased demand for further improving such that it is well compatible with such copying machines and it can stably and continuously provide an output having a further improvement not only in terms of the image quality but also in terms of the product quality.
Besides, in recent years, users of copying machines often have cared about the spaces occupied by the copying machines in order to make effective use of the limited space of an office for office works.
In consequence, it is necessary for the copying machine to be miniaturized, and along with this, it is indispensable for the electrophotographic light receiving member used therein to be also miniaturized It is necessary for such small electrophotographic light receiving member to be have a indeed improved performance and to be capable of being provided at a reasonable production cost.
The present invention is aimed at solving the foregoing problems in the prior art and providing an improved film-forming method and apparatus which enable to efficiently form a high quality deposited film having excellent characteristics, which satisfy the foregoing demands.
Another object of the present invention is to provide an improved film-forming method and apparatus which enable to stably afford a high quality deposited film having excellent characteristics, which can be desirably used in the production of a semiconductor device such as a semiconductor circuit element, electrophotographic light receiving member, image input line sensor, image pickup device, photovoltaic device, or the like, at a reasonable production cost.
A further object of the present invention is to provide a film-forming apparatus comprising a reaction chamber capable of being vacuumed and having a reaction space in which a plurality of substrates are capable of being arranged on a common circumference so as to establish an inner space circumscribed by said plurality of substrates, and a means for introducing a film-forming raw material gas into said inner space, wherein a first electrode for supplying a high frequency power into said inner space is provided at a central position in said inner space circumscribed by said plurality of substrates, a second electrode is provided outside said plurality of substrates arranged on said common circumference, and a shielding member at least a part of which being constituted by a dielectric material is provided between said second electrode and said plurality of substrates arranged on said common circumference such that said shielding member substantially shields said film-forming raw material gas so that said film-forming raw material gas is confined inside said shielding member and transmits a high frequency power supplied to said second electrode into said inner space.
A further object of the present invention is to provide a film-forming method comprising the steps of spacedly arranging a plurality of substrates on a common circumference in a reaction chamber capable of being vacuumed so as to establish an inner space circumscribed by said plurality of substrates in said reaction chamber, introducing a film-forming raw material gas into said inner space, and applying a high frequency power into said inner space, whereby plasma is generated to cause the formation of a deposited film on each of said plurality of substrates, wherein a first electrode is arranged at a central position in said inner space circumscribed by said plurality of substrates, a second electrode is arranged outside said plurality of substrates arranged on said common circumference, and a shielding member at least a part of which being constituted by a dielectric material is arranged between said second electrode and said plurality of substrates arranged on said common circumference to substantially shield said film-forming raw material gas so that said film-forming raw material gas is confined inside said shielding member and transmit a high frequency power supplied to said second electrode into said inner space while applying a high frequency power to said first electrode, whereby plasma is generated in said inner space to cause the formation of said deposited film on each substrate.